Development of Unmanned Aircraft System and Its Use in Investigating the Impact of Pre-Existing Airmass Boundaries on Supercell Rotation

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Intellectual Merit: The purpose of this project is to develop and utilize unmanned aircraft systems (UAS) to obtain critical meteorological observations aloft in the vicinity of severe thunderstorms. This is an exploratory project with the initial emphasis being on the system development and obtaining experience in utilizing such systems in severe storm environments. The UAS will then be used to collected data during the second Verification of the Origins of Rotation in Tornadoes Experiment (VORTEX 2). An examination of the impact of pre-existing airmass boundaries on supercell rotation serves as an important component of the VORTEX 2 objectives. Observations made during the first VORTEX clearly revealed the significant role that preexisting airmass boundaries (boundaries that are not generated by the storm itself) can play in the enhancement of supercell rotation. However, there are many unanswered questions regarding the precise nature of supercell-boundary interactions. These questions have so far remained virtually unanswerable largely due to insufficient thermodynamic measurements above the surface. Airmass boundaries can be localized regions of enhanced horizontal vorticity, enhanced convective available potential energy, and dynamically-driven upward motion. Each of these properties could impact supercell rotation. The specific aim of the experiments is to quantify these properties in order to determine how 1) horizontal vorticity and 2) dynamically/thermodynamically-driven vertical motion impact the rotation of a supercell interacting with a preexisting airmass boundary. The analysis required to answer these questions requires data collected through coordinated observations of both the thermodynamic and kinematic properties of airmass boundaries and nearby storms. Data collected during previous field programs dealing with supercells and tornadoes are insufficient to enable this analysis. However, observations in VORTEX 2 potentially will provide a unique opportunity to collect these coordinated data. The analysis requires four dimensional (4D) wind fields of preexisting boundaries and nearby storms as well as the temperature and moisture fields across these boundaries. In the VORTEX 2, the 4D flow fields will be retrieved with multiple Doppler radars and the detailed thermodynamic structure of airmass boundaries will be retrieved using the developed UAS and a mobile mesonet vehicle. Broader Impacts: This work will stimulate and support the development of advanced instrumentation. Better understanding of how supercell rotation will respond to a specific storm-boundary interaction potentially will benefit society through better forecasts of tornado genesis.